The generic class of materials covered by substantially random α-olefin/vinyl aromatic monomer interpolymers, and especially ethylene/styrene interpolymers (“ESI”) and ethylene/propylene/styrene interpolymers (“EPS”) and are known in the art. They offer a range of material structures and properties which makes them useful for varied applications, such as compatibilizers for blends of polyethylene and polystyrene as described in U.S. Pat. No. 5,460,818. Although of utility in their own right, Industry is constantly seeking to improve the applicability of these interpolymers. Such enhancements may be accomplished via additives or the like, but it is desirable to develop technologies such as blend systems to provide improvements in processability and/or performance without requiring further addition of other additives.
One area where such advantages can be manifested is in blends of these interpolymers with propylene-based polymers. Propylene homopolymers and copolymers are used in a wide range of applications where stiffness is required. However such polymers are often lacking in impact resistance, can be difficult to fabricate, and often exhibit significant stress whitening. Historically poly (vinyl chloride), (PVC) has been used for applications requiring such combinations of properties and, in addition, as is required for certain applications, PVC is also able to impart specific haptics or “touch and feel”. However, PVC is increasingly under scrutiny due to environmental concerns.
Other attempted solutions to this problem have involved the preparation of blends of propylene homopolymers and copolymers with for instance ethylene/α-olefin copolymers to improve impact resistance. However such blends typically have poor optical properties due to the incompatibility of the individual blend components and also do not have the desired haptics of PVC.
In addition, solutions have been proposed which have involved blending propylene homopolymers and copolymers with polymers containing styrenic functionality (known to deliver PVC-like haptics). For instance, JP 10/60194 describes blend compositions consisting of 50-99 wt percent propylene homopolymer or copolymer and 1-50 wt percent of an ethylene/vinylidene aromatic monomer copolymer; (consisting of 50-97 mol percent ethylene and 3-50 mol percent vinylidene aromatic monomer). Proposed advantages of such blends were high surface hardness, excellent mar resistance and a good balance with impact strength.
In addition, JP 10/273566 discloses an olefinic resin composition of 1-99 wt percent propylene homopolymer or copolymer having a refractive index 1.490 to 1.510 at 25° C. and 1-99 wt percent of a copolymer of a vinyl aromatic monomer with ethylene or a C3-C20 alpha olefin having a refractive index 1.490 to 1.510 at 25° C. The refractive index of the vinyl aromatic copolymer matched that of the polypropylene. In addition, blends consisting of terpolymers were also produced with ethylene, styrene plus either 1-butene, 1-hexene or 1-octene.
JP 07316356 A describes a soft polypropylene-based resin composition with high transparency and softness, consisting of 5-70 wt percent of a crystalline polypropylene and 30-95 wt percent of an ethylene/styrene/α-olefin elastomer having from 0.01 to 30 mol percent styrene and at least 30 mol percent of a C5 or greater α-olefin. The resin composition has high softness, transparency and impact, whitening and cold resistance.
JP 07316355 A also describes a soft polypropylene resin composition consisting of 5-70 wt percent of a crystalline polypropylene and 30-95 wt percent of an ethylene/styrene/1-butene elastomer having from 0.01 to 30 mol percent styrene and at least 45 mol percent 1-butene. The resin composition has high softness, transparency and impact, whitening and cold resistance.
JP 07330982 A describes a thermoplastic resin composition with high resistance to compression set-comprising 1) polypropylene resin, 2) ethylene/α-olefin copolymer rubber and 3) ethylene/styrene/α-olefin copolymer. Also claimed was a process for preparing the composition in which 2) was crosslinked under a shearing process while 1) is melted. The crosslinked composition had high resistance to compression set.
JP 10/87918 describes a resin composition consisting of 1-99 wt percent propylene homopolymer and/or propylene copolymer, and 1-99 wt percent of an ethylene/vinyl aromatic copolymer; with 1-55 mol percent vinyl aromatic content with a specific stereo regular alternating structure. The resin composition was claimed to be superior in a balance of toughness/stiffness for use in electronic, electrical parts, injection-molded articles, film pipe or other applications
Blends of hydrogenated random styrene butadiene rubber and polypropylene have also been used for such applications. However the hydrogenated SBR blend component is expensive given the required hydrogenation step after polymer formation.
The above references, whilst generally providing useful blend compositions, do not address the specific merits in terms of unique combinations of material properties that have been found in the current invention for fabricated articles produced from blends of substantially random ethylene/propylene/vinyl aromatic monomer interpolymers with propylene homopolymers or copolymers. Thus it would be highly advantageous to have available fabricated articles, such as a sheet or film having good haze (<15 percent for a 0.38 mm (15 mil) thickness film) while exhibiting enhanced toughness and heat resistance and significantly less whitening when subjected to stress. In addition it would also be highly advantageous if such films could exhibit “PVC-like” haptics while being prepared from a styrenic polymer, the preparation of which does not require the expensive hydrogenation step.